The present invention generally relates to communication protocols and more particularly to a communication protocol for establishing a connection and data transferring between a server and a remote device over a communication network using an acoustically coupled modem.
E-mail has become ubiquitous in our society today. It spans the personal and professional world, and many users have e-mail accounts for both work and home. People use it to conduct business, and keep in touch with loved ones. For some it has become more useful than the telephone and post office combined. It is considered the xe2x80x9ckiller appxe2x80x9d of the Internet. Embodiments of this invention bring email to users who otherwise might not have access.
But for all its virtues, e-mail typically requires a computer with an Internet connection to send and receive messages. This limits the availability of e-mail to the business or pleasure traveler, or for those in locations with no Internet access. Laptop computers provide a solution for some, but they are expensive, costing in the thousands of dollars. While they may accompany some business travelers, they tend to be awkward and bulky and often are left behind, and are certainly of limited use on vacation. Also, while the Internet may be reached from many locations, it is not universal, and toll charges may apply. A simple phone line connection is much easier to access.
Palmtop computers, such as those made by Palm, Inc., provide an excellent portable computing device for both corporate and vacation travelers. Other PDAs (Personal Digital Assistants) may be used. Alternately a portable stand-alone device can be configured to send and receive messages. For example, a portable device having a keyboard for data entry, and a screen for viewing text and possibly images could be used.
What is needed therefore, is a method and apparatus for sending and receiving e-mail on a palmtop or other device using a phone line.
A method and apparatus for establishing a connection between a server and a remote device over a communication network is provided by embodiments of the present invention. Data transmission is attempted at a first carrier frequency and bit rate. If transmission is unsuccessful, the bit rate is lowered. In one embodiment the bit rate is lowered by changing the modulation type. If transmission remains unsuccessful, the carrier frequency is changed to a second carrier frequency. As data transmission continues, the bit rate may be interactively increased or decreased in order to maximize data transfer throughput.
A connection is first attempted using the highest carrier frequency and the highest bit rate supported by the specific embodiment. If a connection is not made, or errors occur, the remote device will drop the bit rate. If a connection is still not made, the bit rate is cut again. If a connection remains illusive, the carrier frequency is changed.
Various phones perform differently with different carrier frequencies. For example, older cellular phones work better with a lower carrier, while analog phones prefer with a higher carrier. New mobile digital phones have improved overall frequency response, and work well with both.
Once a connection is made, the telephone network channel characteristics may change. To account for this, and to optimize the data throughput, the bit rate may be interactively changed by varying the modulation scheme. For example, if QPSK is being used, and no errors occur for a number of data transfers, the modulation type is changed to 8PSK. If the channel changes such that this modulation cannot be sustained, it is dropped back to QPSK, and data transfer resumes.
The data transfers are used by one embodiment of the present invention to send and receive e-mail messages. Alternately, other types of data for other applications may be sent using similar embodiments.
A better understanding of the nature and advantages of the present invention may be gained with reference to the following detailed description and the accompanying drawings.